Hi aaaxton
I've been playing around with you proposed itinerary (I have lots of time on my hands )
The Alaska flights are definitely what is causing your itinerary to fail with the online tool
When I enter the following flight segments:
...
SFO-ANC
ANC-SEA
...
I get the same error as you got.
Changing ANC-SEA to PDX-SEA gives me an itinerary that can be completed, and priced up
It is of course not what you want, and adds an extra segment to the itinerary (the surface segment ANC-PDX)
But at least it gives you an itinerary you can play with while you explore your options
And when the times comes, and you change PDX back to ANC, you'll have a valid itinerary that can be ticketed by a travel agent or direct with an airline.